The present invention patent refers to and discusses a manufacturing process for cans for foodstuff packing, equipping them with efficient means so that the vacuum closing thereof is obtained by easily removable unclinched metal covers and with out the help of any mechanical closing means such as: threads, nippers, screws, etc.
The inventive idea essentially consists of providing the tinned sheet cans, used for packing preserved food and other foodstuff and usually formed by three pieces, namely: cylindrical body, cover and bottom end applied by clinching, with suitable and efficient devices to receive an easily removable metal cover, the closing of which is carried out without clinching or other mechanical devices, i.e., merely by the action of vacuum which is formed inside the packings during the processing of products, either by physical vacuum obtained during the cooking or sterilization processes of products in water-bath or by mechanical vacuum, when relating to dried products.
For better understanding the invention we should observe that the easily removable cover, by which and thanks to the present invention, cans of this type shall then be closed, consists of an easily removable cover which is the object of patent application no. U.S. 07/888,175, dated May 26,1992, now U.S. Pat. No. 5,275,679 by the same inventor, the application and use of which is being effected with excellent results for closing cups and other glass packings in substitution for the closing systems by clinching.
These easily removable metal covers mentioned herein for clarification purposes and for a better understanding of the present invention, of which they are not a part, are usually formed by a circular panel equipped with a lowering flange or skirt, having close to its internal surface a circular groove with a sealing gasket made of a resinous material (plastisol), and presenting at the center of its panel a basin-shaped region, centrally equipped with a relief hole, which is locked by a detachable seal made of the same resinous material of the gasket and when this seal is detached for opening the packing for the first time such procedure causes the rupture of the vacuum created inside the packing and subsequently opening or releasing the cover without making any effort or using tools by the operator engaged in the opening thereof.